Humans care about morality. Yet, they often engage in actions that contradict their moral self. Unethical amnesia is observed when people do not remember or remember less vividly these actions. This paper explores two reasons why individuals may experience unethical amnesia. Forgetting past unethical behavior may be motivated by purely hedonic or affective reasons, such as the willingness to maintain one’s moral self-image, but also by instrumental or strategic motives, in anticipation of future misbehavior. In a large-scale incentivized online experiment (n = 1,322) using a variant of a mind game, we find that hedonic considerations are not sufficient to motivate the forgetting of past cheating behavior. This is confirmed in a follow-up experiment (n = 1,005) in which recalls are elicited the same day instead of 3 wk apart. However, when unethical amnesia can serve as a justification for a future action, such as deciding on whether to keep undeserved money, motivated forgetting is more likely. Thereby, we show that motivated forgetting occurs as a self-excuse to justify future immoral decisions.